1. Field of the Invention
The present invention relates to systems for measuring properties of polymers, and particularly, to a system for measuring glass transition temperature (Tg) of polymers blanketed with a gas phase at high pressures.
2. Description of the Related Art
Glass transition temperature (Tg) of a polymeric material can significantly affect the mechanical properties of the polymeric material. The glass transition temperature is the temperature at which the polymer transitions from a hard, glass-like state to a rubber-like state. The glass transition state is associated with cooperative motion among a large number of chain segments, including those from neighboring polymer chains.
Typically, the glass transition temperature, (Tg), is determined using the following techniques: Differential Scanning calorimetry (DSC); Thermo-Mechanical Analysis (TMA); and Dynamic Mechanical Analysis (DMA). DSC defines the glass transition as a change in the heat capacity as the polymer matrix goes from a glassy state to a rubbery state. This is a second order endothermic transition, requiring heat to go through the transition. Thus, in the DSC measurement, the transition appears as a step transition rather than as a peak transition, such as might be seen with a melting transition. TMA defines the glass transition in terms of the change in the coefficient of thermal expansion (CTE) as the polymer goes from glass to rubber state with the associated change in the free molecular volume. DMA measures the viscoelastic moduli, storage and loss modulus, damping properties, and tan delta of materials as they are deformed under a period (sinusoidal) deformation (stress or strain). The DSC measures a heat flow effect, whereas the TMA is measuring a physical effect, i.e., the expansion in the two directions. Both techniques assume that the effect happens over a narrow range of a few degrees in temperature. However, if the glass transition is very broad it may not be seen with either approach.
In order to make a polymer more flexible and easier to handle, a plasticizer is generally added to the polymer (usually amorphous), which lowers its glass transition temperature. The plasticization effect on polymers is used widely as a processing aid. Due to its ability to plasticize, CO2 at high pressure is widely used for extraction, impregnation, polymerization, foaming and shape forming of polymers.
The assessment of Tg of a polymeric material at high pressure assumes prime importance when a plasticizer, such as CO2, is intended to be used to facilitate processing. In this regard, a real-time technique to monitor the effect of plasticization in-situ and to measure the glass transition behavior of a two phase polymer/gas system at high pressures in the gaseous atmosphere would be useful.
Thus, a system for measuring glass transition temperature (Tg) behavior of polymers at high pressure solving the aforementioned problems is desired.